1. Field of the Invention
The present invention relates to a process for decontaminating soils contaminated by petroleum products. Specifically, the invention relates to a method of treating contaminated soils by applying carbonate salts, ammonium hydroxide, and dilute organic acids to the soil at the site of the contamination. This can be followed by the addition of proteinase enzymes and bacterial inoculates.
2. Description of Related Art
Methods for treating soil contaminated by petroleum and its byproducts are previously known in the art. Such known methods have all had disadvantages relating to the fact that, in most cases, the contaminated soil must be excavated and transported to a decontamination site with a resulting increase in expense and time. Furthermore, most of the methods involve the addition of strong chemicals to the contaminated soil which themselves have the potential of being environmentally hazardous. Additionally, many of the known methods are not able to completely degrade the contaminating substances from soil, but instead, succeed only in separating the most hazardous of the contaminants from the soil in a form in which they can be more easily disposed of.
The Darian et al. patent, U.S. Pat. No. 5,055,196, discloses a process for treating soil or sludge to remove contaminants in contact with the soil or sludge. More particularly, the Darian et al. method relates to a process in which inorganic contaminants, such as metal or metal salts, or organic contaminants, such as PCBs, are removed from water-wet soil and sludge. Darian is apparently limited in its effectiveness to the treatment of soil contaminated with polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins (PCDDs), or polychlorinated dibenzofurans (PCDFs).
In particular, the Darian et al. method relates to both a process and apparatus for treating or cleaning a contaminated water-wet solid containing mixture by contacting the contaminated water-wet mixture with a solvent within an agitating reactor apparatus. The solvent contains a comminuting surfactant. The solvent used in the Darian method is chosen for its ability to dissolve the contaminant and is preferably a hydrocarbon that is sparingly soluble in water. A comminuting surfactant is added to the solvent to form a dispersed mixture of the solids, contaminants, and water. By this means the contaminant can be separated from the water-wet soil or sludge and subsequently the solvents and contaminants are separated and the solvent is reused. Considerable energy is used in the Darian et al. method, commencing with excavation of the contaminated soil and transportation to the Darian apparatus for processing. The transportation of the contaminated materials increases the chance of accidentally spreading the contamination while contributing substantially to the expense of the process. The use of a hydrocarbon solvent also increases the potential for actually creating an environmental hazard where the decontamination process is being performed.
The Smith patent, U.S. Pat. No. 5,039,415, relates to a method of treating hydrocarbon contaminated soil by excavating the soil, forming the soil into a flowing particulate stream; forming an aqueous liquid mixture of water and a microbe-containing solution that reacts with hydrocarbon to form CO.sub.2 and water; dispersing the liquid mixture into the particulate soil stream to wet the particulate; and allowing the substance to react with the wetted soil particulate to thereby form CO.sub.2 and water. The Smith process requires multiple cycles (4+) of the requisite mechanical handling and processing with the microbe-containing liquid mixture. Processes such as the Smith process require months of time and extensive capital investment to accomplish successful remediation of petroleum hydrocarbon soils.
The Gabbita patent, U.S. Pat. No. 4,9 13,586, describes a process and apparatus for safely handling and detoxifying contaminated soil substantially saturated with PH contaminants such as fuel and petroleum hydrocarbons. The contaminated soil is treated with an additive consisting of low grade humic acid and lime that is mixed with the soil in the approximate ratio of nine parts soil to one part of additive. The treatment involves breaking down the contaminated soil particles to a fine silt or sand, mixing the additive into the soil in a tumbler and, finally, discharging the thoroughly additive-covered and encapsulated toxic soil particles into a previously dug trench. In the Gabbita process, the potential for accidental release of the petroleum hydrocarbon contaminant remains should the encapsulation system breakdown. Furthermore the process requires the excavation and transportation of the contaminated soil to another site for treatment and the finding a disposal site for the encapsulated toxic soil.
The Saab patent, U.S. Pat. No. 5,126,073, discloses a method for treatment of solid and fluid materials contaminated by predominantly lipophilic harmful substances, in particular hydrocarbons and the like, especially oil-infested grounds and waters. Saab also discloses suitable systems and emulsifier substances for carrying out the method. The contaminated material is brought into a micro-dispersed, homogeneous emulsion where it is intimately mixed with at least one emulsifying substance as well as possibly with water. Subsequently, the emulsion is separated from the material while water is added and the emulsion is biologically decomposed. The treatment is conducted with an emulsifying composition containing biologically decomposable organic compounds, including a member with emulsification (causing lipophilic and hydrophilic functional groups), a fatty alcohol polyglycol ether-type tenside member and a member having one or more functional groups recognizable by bacterial cell membranes as being absorbable. The Saab method is expensive, time-consuming, labor-intensive and energy-intensive.
The Hoch patent, U.S. Pat. No. 5,149,444, reveals a method for treatment of soil, sediment or sludge containing toxic halogenated organic compounds (such as PCB's) and water. The method comprises the steps of mixing the soil, sediment, or sludge with a reagent (such as polyethylene glycol) capable of reacting with the halogenated compound. The mixture of soil, sediment, or sludge, and reagent is heated in a reaction zone to an elevated temperature thereby forming a reaction zone vapor stream containing at least a portion of the unreacted halogenated organic compound and water contained in the soil, sediment, or sludge. A portion of the reaction zone vapor stream is then condensed under conditions suitable for the formation of a condensate stream containing substantially all of the halogenated organic compound in the reaction zone vapor stream and a vapor stream containing water and trace amounts of the halogenated organic compound. The condensate stream is then recycled to the reaction zone and the resulting vapor stream is then treated to remove trace halogenated organic compound. The so treated stream is vented to the atmosphere; and the soil, sediment, or sludge containing less contaminant is removed from the reaction zone.
The Hoch '444 method's effectiveness is limited to the decontamination of soils, sediments, and sludges containing halogenated organic compounds. Hoch '444 requires the excavation of contaminated materials, relocation of the contaminated material to a reaction kiln, and heating the contaminated soil, sediments, or sludge to 300.degree. C. under pressure to attain a change in state from liquid to vapor. Like Saab, the method is expensive, time-consuming, labor-intensive and energy-intensive. Furthermore, the use of polyethylene glycol introduces an added source of potential environmental hazard.
U.S. Pat. No. 5,008,0 19, the Trost method, is for treatment of water supply contamination. This patent discloses the method of flooding the contaminated formations with an alkaline solution of biodegradable polymers through various injection methods into a contaminated formation to divert, and/or remove contaminants. Decontaminated water is recovered through specific facilities. The Trost method is specifically for the decontamination of existing aquifers. Such decontamination is accomplished by a combination of flooding, injection, extraction and plugging using various alkaline polymer chemicals based on xanthan gum polymer. The extracts resulting from the Trost method must subsequently be treated and disposed of. The Trost method requires subsurface drilling and monitoring capacity along with vast quantities of water and several weeks of time.
The Rose patent, U.S. Pat. No. 5,035,537, discloses a method for treatment of soil, porous rock and similar material contaminated by petroleum, hydrocarbon and volatile organic compounds and includes the steps of gathering the contaminated soil, disbursing it uniformly on an impervious horizontal surface to a depth of four to six inches, treating it with an emulsifying agent and allowing the emulsifying agent to seep through the soil and volatilize the hydrocarbon and organic compounds in the soil. Optionally, the vapors emanating from the soil may be collected and burned.
Rose requires the excavation of contaminated solid materials, transportation of the materials to the site of a horizontal impervious surface where the decontamination process is performed. Furthermore, the Rose method emulsifies the contaminant and purports to volatilize it into the atmosphere both with and without the use of decreased atmospheric pressure. Thus Rose only serves to move the contaminants from the soil to the atmosphere in the hope that dilution with the free atmosphere is alone adequate degradation. Such a method, besides being labor-intensive and energy-intensive, is particularly hazardous in that it allows volatile organic chemicals to evaporate into the environment.
The Bruya patent, U.S. Pat. No. 4,841,998, concerns a method of decontaminating soil in which organic hazardous waste is removed from contaminated soil with an aqueous ammonia solution. The resulting aqueous ammonia solution containing organic hazardous waste is further processed to isolate the organic hazardous waste in a small volume for disposal. The treated soil is then returned to the excavation site without further processing. More specifically, the Bruya patent discloses that a broad range of hydrocarbon based contaminants can be removed from contaminated soil by means of excavation, crushing, screening, mixing with anhydrous ammonia and water (to form aqueous ammonia), settling, centrifugation, extraction of liquid, introduction of a suitable organic solvent, volatilization, extraction of ammonia and solvent by phase separation in which anhydrous ammonia is recycled to the aqueous ammonia mixing tank and the organic solvent is recycled and the extracted concentrate of contaminant is discharged for detoxification processing. As with other known methods, Bruya requires the steps of excavating, crushing and screening which are expensive, time-consuming, energy-intensive and labor-intensive. Furthermore, Bruya requires the handling of potentially dangerous anhydrous ammonia as both a cryogenic liquid and a highly pressurized gas. Additionally, Bruya requires elaborate mechanisms to create aqueous ammonia and then to recycle the ammonia. Additionally, the handling of expensive and potentially hazardous organic solvents such as hexane is also required. The resulting concentrated contaminant extract of the Bruya process must then be transported for final disposal by external means. Data cited in the Bruya process show that multiple treatments may be necessary to decrease the presence of contaminants from concentrations of 1000 ppm to less than 50 ppm.
The Renfro patent, U.S. Pat. No. 5,059,252, discloses a method for enhancing bioremediation which includes the step of applying a cationic ion exchange resin to the contaminated soil in an amount sufficient to promote growth of organisms capable of degrading the hazardous waste. The Renfro method is specifically intended to expedite the growth of certain bacteria and saprophytes and hasten the action of certain bacterial and saprophytic enzymes by acidifying hydrocarbon contaminants using a cationic ion exchange resin mixed with cyclic ring hydrocarbons covalently linked with a mineral acid but does not itself decontaminate or degrade the contaminants in hydrocarbon contaminated soils. The overall effect of the Renfro method is to acidify (decrease the pH of) contaminated soils to reduce the time (months or years) required of the aforementioned biological agents to accomplish bioremediation of the contaminating hydrocarbons. Thus the Renfro method does not directly accomplish decontamination of the soil but simply facilitates the natural bioremediation process which still takes months or years to accomplish.
The Hoch patent, U.S. Pat. No. 5,096,600, discloses a method for substantially degrading and detoxifying soils contaminated with halo organic compounds. The method comprises contacting a soil, sediment, or sludge containing less than 5% by weight of a halo organic contaminant, with a reagent of the formula MX, where M is a metal selected from the group consisting of K, Na, Ca, Zn, Mg, Ba, Pb, and X is hydroxide, carbonate, oxide, or acetate. The contact and subsequent reaction is carried out under conditions that insure the phase compatibility of the halo-organic contaminant and the reagent, which contact and subsequent reaction is preferably carded out under anhydrous conditions. The contact is carried out for a period of time sufficient to effect the dehalogenation of at least 90% of the contaminant.
Hoch '600, is limited in its effectiveness to the dehalogenation of (primarily intensely halogenated) halo-organic contaminants in soil, sediment or sludge. Decontamination by the Hoch method means the substantial removal (at least 90%) of the halogen atoms from compounds in the soil, thus yielding less toxic organic compounds (i.e. dichlorobiphenyl) or completely dehalogenated compounds. The resultant organic compounds are decreased in toxicity but require additional treatment with other processes or agents not a part of the Hoch method to finally render the contaminated soil fully decontaminated. The essential phase compatibility required to accomplish the Hoch method is accomplished by elevating the contaminated soil with the MX reagent to a temperature between one hundred eighty degrees Celsius (180.degree. C.) and two hundred degrees Celsius (200.degree. C.) with a quantity of the following phase compatibility agents and/or aprotic solvents acting in either or both capacities: (a) alcohols, including glycols, polyalkylene glycols, and polyols, (b) nitriles, (c) ethers, including polyethers, cyclic ethers, lower alkyl ethers of glycols, and lower alkyl ethers of polyalkylene glycols, (d) amines, and (e) amides. Without benefit of the above cited phase compatibility agents, the Hoch process requires the contaminated soil and reagent mixture to be elevated to the temperature of three hundred twenty degrees Celsius (320.degree. C.). Thus, the Hoch method does not provide for the final degradation of hydrocarbon contaminants and requires follow-up processing. Furthermore, the method is time-consuming and expensive it requires an additional method of decontamination to break down the dehalogenated hydrocarbons.
The Bruya patent, U.S. Pat. No. 4,906,302, discloses a method for decontaminating the solid material contaminated by organic hazardous material which consists of forming an aqueous ammonia solution effective for removing organic hazardous waste from the contaminated material, contacting the material contaminated with organic hazardous waste with the aqueous ammonia solution to thereby transfer the organic hazardous waste from the material to the aqueous ammonia solution and separating the aqueous ammonia solution containing the organic hazardous waste from the material. Specifically, Bruya '302 discloses a method for decontaminating solids using an aqueous ammonia solution manufactured on site from anhydrous ammonia with an organic promoter (i.e., organic extracting solvent) from the group of pentane, hexane, heptane, octane, mineral oil, fuel off, toluene, Freon 113, 1,1,1-trichloroethane and mixtures of it. Thus, additional hydrocarbon materials are required to be brought into the contaminated site creating additional environmental hazards. Many of the organic promoters proposed by Bruya are demonstrated carcinogens, mutagens, and ozone depleters as well as being quite flammable. In the method as disclosed, it is necessary to recycle the ammonia and the organic promoters with additional procedures in order to avoid further environmental hazard. This recycling involves added time, expense and energy investment.
The present invention overcomes many of the various disadvantages encountered in methods known in the art, such as those described above, which have been used to decontaminate soil contaminated by hydrocarbons. The present invention's method of hydrocarbon decontamination of soils is principally accomplished by chemical breakdown of hydrocarbons. The decontamination can be further enhanced by the addition of protein enzymes. Biological microbes can be additionally added to enhance this decontamination process. The method can be accomplished on-site, thus avoiding the necessity of transporting the contaminated soil to another site. Chemical breakdown of the total parts of petroleum hydrocarbon occurs swiftly. Such breakdown can be continued by means of the proteinase enzymes and bacterial inoculate. Thus, the formerly contaminated soil becomes harmless to plant life within hours of treatment. Hydrocarbons treated with the process of the present invention are transformed into a water soluble state in which no toxic levels of hydrocarbons are detected. The process not only degrades toxic materials but does not render the soil sterile. Furthermore, the chemicals added to the soil to accomplish the decontamination are themselves biodegradable. Any hydrocarbon materials left over from the process are rendered more available to bacteria (both indigenous and otherwise) for further breakdown of the total parts of hydrocarbon. Thus, soil treated with the process of the present invention is left in a nutrient rich state for breakdown by bacteria, fungi and higher forms of plant life.